1. Field of the Invention
The present invention relates to paper-making machines and, more particularly, to paper-making machines having air assisted threading doctor elements.
2. Description of the Related Art
Machines for making sheets of material, especially paper, utilize an array of rotating longitudinal cylinders or rolls on which the paper travels. The rolls are used in a variety of different sections during the paper making process. One of the sections is a dryer section, which may consist of several dryer sections, situated one after another. In a dryer section, as the name implies, incoming wet paper is dried by drying rolls.
In most of the various segments of the paper machine, it is known to provide a doctor element, such as a doctor blade, which bears against a roll of the section and cleans the roll by scraping off residual fibers or the like. A water shower is typically provided in association with the doctor blade for lubricating the doctor blade as it bears against the roll. The shower directs a stream of water against the roll across the width of the doctor blade and on the approach side of the doctor blade.
In sections such as a dryer section, it is known to provide a threading doctor at the beginning of a roll in order to direct the paper onto the roll. As the paper advances along the particular section, the threading doctor associated with each roll directs the paper onto the next roll. Generally, such threading doctors have air blowing systems that direct flowing air from nozzles into the region where the paper is to separate from the roll and advance to the next roll. The blowing air forces the paper to travel away from the roll and into a convergence area of the next roll for pickup by that next roll. The use of blowing air is an efficient way to direct the advancing paper since the paper generally advances at 4,000 to 6,000 feet per minute (fpm).
However, the problem with such threading systems is the enormous air pressure required to continuously supply each blowing system associated with each roll. As an example, a typical dryer group of a dryer section includes ten (10) dryer rolls each with a blowing system having an approximate twenty (20) CFM (Cubic Feet per Minute) air flow, yielding approximately two-hundred (200) SCFM. With as many as three (3) to twelve (12) dryer groups per dryer section, this may require an air supply system of six hundred (600) to two-thousand four-hundred (2,400) SCFM.
What is thus needed is an air threading system that utilizes an air supply system of considerably less SCFM.